Status: this preprint was under review for the journal OS but the revision was not accepted.
Restoration of the Baltic Proper by decadal oxygenation of the deepwater
Anders Stigebrandt
Abstract. Sediment core data from the Baltic Proper show that deepwater sediments during the present brackish state have alternated between anoxic and oxygenated episodes, implying that anoxic episodes were shut off by a natural restoration mechanism. This mechanism is identified as sustained oxygenation of the deep bottoms which shuts off the internal phosphorus (P) source from anoxic sediments. When this happens, P sink processes rapidly reduce the winter surface concentration c1 of P. A P budget model shows that the presently eutrophic Baltic Proper can be restored in about 10 years by man-made (or natural) sustained oxygenation of the deepwater. This will reduce the total P supply and c1 to about 25 % of present day values and the oxygen demand in the deepwater will be reduced proportionally, meaning that the natural water exchange again should be able to oxygenate the Baltic Proper and the restoration equipment can be removed.
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Sediment core data reveal that the Baltic Proper has switched rapidly from eutrophic and oligotrophic state. Switches are connected to weakening of the vertical deepwater stratification caused by rarely occurring extended periods lacking large inflows of new deepwater. The internal phosphorus (P) source from anoxic bottoms is then shut off and the total P supply decreases drastically. A P budget model shows that the surface layer P concentration will decrease drastically.
Sediment core data reveal that the Baltic Proper has switched rapidly from eutrophic and...
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